Passive seat belt systems include a seat belt and means for automatically moving the seat belt into position about a vehicle occupant without manipulation by the occupant. Such systems generally comprise a track extending adjacent to the vehicle door from a forward position to a rear position adjacent to the back of the seat, and a seat belt anchor which is slidable in the track. The seat belt anchor is connected to a flexible tape which is driven to cycle the anchor between the forward and rear positions. A shoulder belt attached to the anchor is thereby driven between an open position forward of the seat and a secured position to the rear of the seat. An emergency lock is normally associated with the rear end of the track to retain the seat belt anchor in the secured position in an emergency.
Various types of emergency locks for passive seat belt systems are known. For example, U.S. Pat. No. 4,345,781 shows a passive seat belt system wherein an emergency lock housing is mounted to the side of the track between the forward and rear ends of the track. A pair of pivotal arms are spring biased together to extend partially from the lock housing into the track, with one arm in the path of movement of the driven tape and the other arm in the path of movement of the seat belt anchor carried with the tape. The two pivotal arms are arranged such that the seat belt anchor cannot move forward past the lock housing unless a lost motion clearance between the anchor and the tape allows the driven tape first to move the associated pivotal arm out of its path of movement. That pivotal arm simultaneously moves the other pivotal arm out of the path of the anchor.
This type of lock functions effectively in emergency situations, but suffers from disadvantages associated with the lock housing. The housing must be large enough to contain both pivotal arms, as well as a spring and a pivot bar which connects the two arms for movement together about the pivot bar axis. The housing is located outside the track to one lateral side thereof to receive the pivotal arms when not in the locking position. This arrangement complicates the structure and configuration of the passive seat belt system. Furthermore, the locking components of a passive seat belt system are contained within the structure of the B-pillar of the vehicle at the outboard side of the seat. The housing outside of the sliding track consumes valuable space in the B-pillar structure and presents an obstacle to vehicle designs which call for a reduction in size.
Another emergency lock for a passive seat belt system is shown in U.S. Pat. No. 4,302,031 wherein a locking mechanism is mounted in a housing located at the rear end of the track. A tape extends beyond the end of the track through the housing to a driving motor, and a seat belt anchor carried on the tape is blocked from movement beyond the end of the track by a stop surface on the housing. A spring biased locking lever is pivotally mounted to the housing with a locking end thereof extending outside of the housing, and a releasing end extending inside the housing in line with the terminal end of the track. The locking end of the lever engages an external member of the seat belt anchor when the tape carries the anchor and an attached belt into a secured position at the end of the track. The releasing end of the lever is engaged by a release block carried on the tape to pivot the locking end out of engagement with the seat belt anchor when the tape is driven back in the opposite direction through a lost motion clearance with the seat belt anchor. This type of lock functions effectively, but also suffers from the disadvantage of presenting a structure which is complicated and which consumes valuable space outside of the sliding track.